Passive solar system in Japan

Passive solar system in Japan

WREC 1996 PASSIVE SOLAR SYSTEM IN JAPAN Akio O K U M U R A 3-16-19 Nakamurakita, Nerima-ku, Tokyo 176, JAPAN The 'OM Solar System' is the most wi...

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WREC 1996

PASSIVE SOLAR SYSTEM IN JAPAN

Akio O K U M U R A 3-16-19 Nakamurakita,

Nerima-ku,

Tokyo 176, JAPAN

The 'OM Solar System' is the most widely used l o w - e n e r g y a r c h i t e c t u r e system in Japan. The system has been e m p l o y e d in a p p r o x i m a t e l y 8,000 homes and in over 40 public b u i l d i n g s w i t h i n the past eight years. The system is e x t r e m e l y simple. Basically, it is a c o m b i n a t i o n of the roof which s i n g l e - h a n d e d l y acts as the heat collector, the intake of fresh air and its inflow u n d e r n e a t h the roofing, and the heat storage of concrete slab under the floor. Together, these elements work as an e f f e c t i v e floor h e a t i n g and air v e n t i lation system. M a r k e d by flexibility, the system allows n u m e r o u s v a r i a t i o n s to serve m u l t i - f u n c t i o n a l purposes. These range from an access to a hot water supply and the d e h u m i d i f i c a t i o n by n o c t u r n a l r a d i a t i o n in hot climates, to p h o t o v o l t a i c power g e n e r a t i o n and the u t i l i z a t i o n of rainwater. 'OM Solar' is c o m p o s e d of two organizations: The OM Solar A s s o c i a t i o n (Co., Ltd.), c o m p r i s i n g 350 local c o n s t r u c t i o n companies, and the OM Institute (Co., Ltd.), e m b o d y i n g a large number of a r c h i t e c t s and researchers. W h i l e each of the two o r g a n i z a t i o n s has a distinct role to perform, they work in concert to reach beyond the t e c h n o l o g i c a l d e v e l o p m e n t and the c o n s t r u c t i o n work of their domain, to a c t i v e l y involve those outside their circle, i n c l u d i n g material suppliers and the consumers themselves, in an effort to p r o l i f e r a t e a style of living using the passive solar system. The J a p a n e s e a r c h i p e l a g o is a long arc of islands e x t e n d i n g from n o r t h e a s t to southwest. Because of the s u r r o u n d i n g seas and the m o u n t a i n o u s c o n f i g u r a t i o n of the land, the climate of Japan is c h a r a c t e r i z e d by large d i f f e r e n c e s both r e g i o n a l l y and season~ly. This d i v e r s i t y has p r o d u c e d a fine n e t w o r k of w e a t h e r o b s e r v a t i o n stations that p r o v i d e an a b u n d a n c e of m e t e o r o l o g i c a l data. At OM Solar, w e a t h e r data c l a s s i f i e d by the time of day is p r e p a r e d s p e c i f i c a l l y for the passive system by e x t r a c t i n g r e l e v a n t data c o m p i l e d over the past ten years from 839 m e t e o r o l o g i c a l observ a t i o n points i n s t a l l e d (in 20-kilometer mesh) t h r o u g h o u t Japan. This data is fed into a computer s i m u l a t i o n system, e x c l u s i v e l y for the use of the OM Solar System, to assess houses and b u i l d i n g s for i m p r o v e m e n t s to be made in design and for their estimates of performance. The f o l l o w i n g is a closer look at the OM Solar S y s t e m from its three p e r s p e c t i v e s o u t l i n e d above. 66

WREC 1996 THE SYSTEM AND ITS M U L T I - F U N C T I O N A L V A R I A T I O N S In Japan, the great m a j o r i t y of houses are d e t a c h e d single units, m o s t l y m a d e of wood. In the u r b a n areas, where the plots of land on which these houses stand are s e v e r e l y r e s t r i c t e d in size, the amount of s u n s h i n e b e s t o w e d upon the first floor is most often inadequate. Due to the r e g u l a t i o n s r e s t r i c t i n g the height of the b u i l d i n g s in each area, however, there is g e n e r a l l y a s u f f i c i e n t amount of s u n s h i n e on the roof. For this reason, the OM Solar System u t i l i z e s the roof for heat collection, the basis of its operation. In houses made of wood, the c o n c r e t e slab on the first floor p r i m a r i l y acts as the body for storing a c c u m u l a t e d heat. The air acts as the m e d i u m for t r a n s p o r t i n g heat collected on the roof to the heat s t o r i n g s e c t o r s of the building. In the OM Solar System, the roof with a s o u t h e r n e x p o s u r e serves as solar collector. Heat is c o l l e c t e d on the roof itself and c o n v e y e d by an i n f l o w of o u t s i d e air through a layer of space d i r e c t l y b e n e a t h the roofing. (See Fig. I: OM Solar System.) The roof c o l l e c t o r is o r d i n a r i l y c o m p o s e d of two sections. On the lower part of the roof nearer the eaves is the sheet metal r o o f i n g with the space u n d e r n e a t h for the airflow, that f u n c t i o n s as the p r e - h e a t i n g section of the h e a t - c o l l e c t i n g process. F u r t h e r above and away from t h e : e a v e s is the h i g h - t e m p e r a t u r e c o l l e c t i n g section, which c o n s i s t s of a metal r o o f i n g covered with a sheet of glass and a space for s t a g n a n t air underneath. Fresh air passes through a space under the roof-top, t h e r m a l -

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Fig.1 OM Solar System 67

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WREC1996 i n s u l a t e d from the rooms below, and enters the layer of space from the lowest edge of the p r e ' h e a t i n g section and flows upward. At the upper end of the h i g h - t e m p e r a t u r e c o l l e c t i n g section, the air is led through a ridge duct to a c c u m u l a t e in the r o o f - t o p air chamber. The heated air from the ridge duct then enters the fan-box, an air h a n d l i n g unit e q u i p p e d with dampers on two sides to r e g u l a t e the d i r e c t i o n of the airflow. (See Fig. 2, d i a g r a m I.) In the wintertime, a fan forces the air to flow down the v e r t i c a l air duct to the space under the floor. A thermal sensor i n s t a l l e d at the j u n c t i o n of the hightemperature c o l l e c t i n g section and the ridge duct controls the on-off switch of the fan and the volume of air supply. The c o m b i n a t i o n of the two h e a t - c o l l e c t i n g sections best suited to a house or a building, and the s q u a r e - m e a s u r e and the length of the h i g h - t e m p e r a t u r e section in particular, is d e t e r m i n e d by computer simulation, based on the data that includes the a m o u n t of solar radiation, the angle of the roof, the h e a t i n g load, and the t h e r m a l - s t o r a g e c a p a c i t y of each case. Ordinarily, the floor consists of a f i n i s h e d wooden floor, an a i r - s p a c e underneath, and either a c o n c r e t e bed or a c o n c r e t e slab to store the heat. The h e a t e d air coming down the v e r t i c a l duct first diffuses in an e x p a n d e d p i t - l i k e area in the airspace, then travels through the layer of space b e t w e e n the floor and the c o n c r e t e - - a layer ranging from s e v e r a l c e n t i m e t e r s to no more than 2 0 - c e n t i m e t e r s high. Due to the d i f f e r e n c e s in thermal c o n d u c t i v i t y and the thermal c a p a c i t y b e t w e e n wood and concrete, the heat is p r i m a r i l y t r a n s f e r r e d to the c o n c r e t e to be stored there. In the final step, the heated air is d i f f u s e d inside the room through an outlet located g e n e r a l l y near a window. Not only does the s y s t e m p r o v i d e v e n t i l a t i o n while the h e a t is being collected, but it also m a i n t a i n s a 'plus' room air pressure, 2.) Over-heating in wintertime: heat exchange to hot water

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WREC 1996 h e l p i n g to keep the draft from entering. An o p e n - s p a c e d e s i g n for the interior is r e c o m m e n d e d w h e n e v e r possible, as open staircases and d o u b l e - h e i g h t ceilings help the n a t u r a l c u r r e n t s b e t t e r d i s t r i b u t e the heat t h r o u g h u n i n t e r r u p t e d space. E x c e p t in coldclimate regions that call for a i r t i g h t designs, the internal air p r e s s u r e causes an o u t f l o w of air t h r o u g h tiny cracks for a hand in air v e n t i l a t i o n . When the room t e m p e r a t u r e rises above a set degree, the sensor gives p r i o r i t y to the use of hot air for o b t a i n i n g a hot water supply by air h e a t - e x c h a n g e . Inside the fan-box, there is a h e a t - e x c h a n g e coil c o n n e c t e d to a c o n d u i t to the hot water tank. (See Fig. 2, d i a g r a m 2.) The pump c i r c u l a t e s the water which acts as a m e d i u m for the hot air, p r e v e n t i n g o v e r h e a t i n g . Cooler air with its heat taken out can now be sent to its d e s i g n a t e d space under the floor. Once the heat is no longer a v a i l a b l e on the roofs, the fan stops and the damper situated at the front of the fan-box shuts down, cutting off its c o n n e c t i o n to the roof c o l l e c t o r s and o p e n i n g the way to the room interior. The heat stored in the c o n c r e t e bed c o n t i n u e s to r a d i a t e a g e n t l e w a r m t h through the f i n i s h e d floor. When the room t e m p e r a t u r e drops b e l o w the set d e g r e e on the sensor, the coil inside the fan-box switches so that it is conn e c t e d to the a u x i l i a r y h e a t i n g boiler, whose job is to heat the c i r c u l a t i n g air and send it to its space under the floor. (See Fig. 2, d i a g r a m 3.) This p r o c e s s also takes place w h e n e v e r heat that is c o l l e c t e d on the roof is not enough to a d e q u a t e l y heat the room w i t h o u t the aid of an a u x i l i a r y heater. In the summer and the t r a n s i t i o n a l seasons when interior h e a t i n g is not necessary, the d a m p e r s i t u a t e d in the b a c k of the fan-box opens toward the e x h a u s t air duct c o n n e c t e d to the outside. (See Fig. 2, d i a g r a m 4.) D u r i n g the day, this works to get rid of the heat c o l l e c t e d on the roof and under the rooftop. At the same time, a hot water s u p p l y . i s o b t a i n e d by the process of heatexchange. With the e x c e p t i o n of Hokkaido, the n o r t h e r n m o s t island, the summers in Japan are hot, humid, and u n c o m f o r t a b l e . One way to allay the d i s c o m f o r t is to select the system's mode that takes a d v a n t a g e of the r a d i a t i o n a l c o o l i n g at night. When the t e m p e r ature o u t s i d e goes b e l o w the room t e m p e r a t u r e , the fan turns back on, first to get rid of the heat r e m a i n i n g under the roof and inside the ridge duct, t h r o u g h the e x h a u s t duct. (See Fig. 2, d i a g r a m 5.) Once the t e m p e r a t u r e inside the ridge duct reaches b e l o w the room t e m p e r a t u r e , the d a m p e r s i t u a t e d in the back of the fan-box opens up on the side of the v e r t i c a l duct, g u i d i n g the air c o o l e d and d e h u m i d i f i e d by n o c t u r n a l r a d i a t i o n down the duct to the space under the floor, c o o l i n g the r o o m and e x p e l l i n g the humidity. (See Fig. 2, d i a g r a m 6.) The sunny and clear w e a t h e r the next day works s p e e d i l y to get rid of any r e s i d u a l m o i s t u r e under the roof. For r a d i a t i o n a l c o o l i n g at night, it is the p r e - h e a t i n g section that p r i n c i p a l l y does the work. The above gives an o v e r a l l view of the m e c h a n i s m of the OM Solar System. However, n u m e r o u s v a r i a t i o n s exist to take into a c c o u n t such factors as the climate of the region, the p u r p o s e of the building, the size of the project, the type of structure, and

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WREC1996 the kind of a u x i l i a r y heating system. In addition, there is an i n c r e a s i n g number of other functional options that can be used in c o m b i n a t i o n with the solar system. Since the structure of the roof in this system from that of an o r d i n a r y roof, it is sometimes collect rainwater. The computer simulation is cases for c a l c u l a t i n g the suitable c a p a c i t y of based on the area's pattern of rainfall.

is no d i f f e r e n t e m p l o y e d to e f f e c t i v e in such the water tank,

Moreover, by using an amorphous solar cell on the roof collector, it is p o s s i b l e to g e n e r a t e e l e c t r i c i t y with no s u b s t a n t i a l b e a r i n g upon the amount of heat collected. In this case, the air p a s s a g e w a y under the heat collector is used for the wiring. S i m u l t a n e o u s l y o b t a i n i n g one's own supply of heat and e l e c t r i c i t y presents a d e f i n i t e a d v a n t a g e in terms of the c o n s t r u c t i o n and the expenses involved, as well as from the standpoint of design. It should be noted also that as such highly s e l f - s u s t a i n i n g buildings are bound to prove strong in the face of c a t a s t r o p h i c disasters, there is now a greater interest toward the system's i m p l e m e n t a t i o n in public buildings.

THE O R G A N I Z A T I O N AND ITS A C T I V I T I E S As a l r e a d y mentioned, 'OM Solar' consists of two organizations, the OM Solar A s s o c i a t i o n (Co., Ltd.), c o m p r i s i n g local construction companies, and the OM Solar Institute (Co., Ltd.), made up of a r c h i t e c t s and researchers. For the p r o l i f e r a t i o n of a passive system f u n d a m e n t a l l y d e p e n d e n t on w e a t h e r conditions and diverse cultures indigenous to specific environments, the OM A s s o c i a t i o n opted to create an o r g a n i z a t i o n of local builders. Currently, some 350 such small c o n s t r u c t i o n companies from across the nation have joined the m e m b e r s h i p of the n o n r i g i d l y b i n d i n g v o l u n t a r i s t chain. The scope of its a c t i v i t i e s e n c o m p a s s e s the following: a c q u i r i n g the basic technology on the use of the OM Solar System and other passive systems, c o n s t r u c t i n g and p o p u l a r i z i n g the system that a c c o m m o d a t e s to specific environments, d e v e l o p i n g c o n s t r u c t i o n skills, p r o v i d i n g technical a s s i s t a n c e to plans by s e l f - g o v e r n i n g bodies, m e a s u r i n g and c o m p i l i n g data, e x c h a n g i n g m a n a g e m e n t and t e c h n o l o g i c a l know-how, and working together in p r o m o t i o n a l activities. The other arm of 'OM Solar', the OM I n s t i t u t e is a l o o s e l y - k n i t group of a large number of architects, technicians, and researchers, w h o s e essential role is to conduct r e s e a r c h - a n d d e v e l o p m e n t on p a s s i v e designs, fundamental technologies, lifestyles, and other related matters. Their p r o j e c t s also include holding study seminars on the t e c h n o l o g y of the s y s t e m and on the use of c o m p u t e r simulation for architects who plan to i n c o r p o r a t e the OM Solar System in their designs, and running a small school for a s p i r i n g students of a r c h i t e c t u r e and skilled workers in r e l a t e d fields. Both the OM A s s o c i a t i o n and the OM I n s t i t u t e r s g r e a t e s t commitment is to arouse consumer interest in l i f e s t y l e s e m p h a s i z i n g the 'renewable', and to provide the public with w o r k a b l e ideas. Toward this end, both o r g a n i z a t i o n s c o n s i s t e n t l y p r o v i d e a large number and a v a r i e t y of p u b l i c a t i o n s on the subject.

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WREC 1996 METEOROLOGICAL

DATA AND THE C O M P U T E R

SIMULATION

SYSTEM

The J a p a n e s e a r c h i p e l a g o , t h o u g h small in terms of land area, s t r e t c h e s from n o r t h to south in l a t i t u d e s c o m p a r a b l e to those of the E u r o p e a n continent. In fact, the n a t i o n s t r a d d l e s a n u m b e r of c l i m a t i c zones from the s u b a r c t i c to the s u b t r o p i c a l . Ocean c u r r e n t s and seasonal winds c o m b i n e with a c o m p l e x m o u n t a i n o u s t e r r a i n to c r e a t e a wide d i v e r s i t y of climates, rich in r e g i o n a l d i f f e r e n c e s and d i s t i n c t l y d i f f e r e n t i a t e d seasons. C o n s e q u e n t l y , m e t e o r o l o g i c a l data are c a r e f u l l y c h a r t e d and p r o v i d e d in abundance. In a d d i t i o n to the 159 w e a t h e r stations, there are 839 A M e D A S (Automated M e t e o r o l o g i c a l Data A c q u i s i t i o n System) u n m a n n e d o b s e r v a t i o n points g a t h e r i n g 4-item m e t e o r o logical data. However, the data from this o b s e r v a t i o n s y s t e m cannot be e m p l o y e d as is in p a s s i v e solar s y s t e m designs and in c o m p u t e r simulation. The OM Solar p r o d u c e s its own system of m e t e o r o l o g i c a l data, e x t r a c t e d from the past 10 years of data b a s e d s t a t i s t i c a l l y on the c o r r e l a t i o n of v a r i o u s w e a t h e r factors s u p p l e m e n t e d by A M e D A S reports. A c c o r d i n g to the daily sum of solar r a d i a t i o n r e c e i v e d at each of the 839 points, the days of the month are d i v i d e d into three groups, for which the a v e r a g e figures are given for the hours of the day. This a m o u n t s to 36 files of data per o b s e r v a t i o n point a year. The w e a t h e r data thus c o m p i l e d is used in the c o m p u t e r s i m u l a t i o n s y s t e m to c a l c u l a t e and a n a l y z e the thermal b a l a n c e of the OM Solar b u i l d i n g being p l a n n e d for specific e n v i r o n m e n t s . The p r i n c i p l e of the OM Solar S y s t e m is simpl e . M a k i n g an a c c u r a t e a s s e s s m e n t of the o u t c o m e from its use is a n o t h e r matter. For this, we rely on the a f o r e m e n t i o n e d c o m p u t e r s i m u l a t i o n system. Each i n d i v i d u a l house or b u i l d i n g is not only c o m p l e x in itself, every one of them is unique. The OM Solar S y s t e m p o s s e s s e s a s i m u l a t i o n s y s t e m e x c l u s i v e l y for its use and a p p l i c a b l e to a wide range or a r c h i t e c t u r a l designing. W e a t h e r d a t a - - y e a r l y or the a v e r a g e figures o v e r a p r e s c r i b e d p e r i o d - - c a n be o b s e r v e d in v a r i o u s graph forms for p r a c t i c a l references. An input of data p e r t a i n i n g to a d e s i g n plan over m y r i a d g r a p h i c d i s p l ~ y s will provide, in a d d i t i o n to the r e g i o n a l w e a t h e r data, further data on i m p r o v i n g the d e s i g n as well as a 'performance estimate, of the d e s i g n in question. Using a material d a t a b a s e to add g r a p h i c details creates a d a t a c a r d s h o w i n g the c o e f f i c i e n t s of o v e r a l l heat t r a n s m i s s i o n - - i n c l u d i n g the h e a t - b r i d g e - - w h i c h can be r e f e r r e d to at the time of data input. All a r c h i t e c t u r e p l a n n i n g to use the OM Solar S y s t e m are first run on the c o m p u t e r s i m u l a t i o n at the d e s i g n i n g stage. After they are built, a c t u a l m e a s u r e m e n t s are m a d e on 2 to 40 h o u s e s and b u i l d i n g s every year to check on the e f f e c t i v e n e s s of b o t h the c o n s t r u c t i o n work and the s i m u l a t i o n system. A final word: N e x t year in H o k k a i d o ' s Kushiro, PLEA 1997 K U S H I R O will take p l a c e from J a n u a r y 8th to 10th, on the theme of 'Sust a i n a b l e C o m m u n i t i e s and A r c h i t e c t u r e - - B i o c l i m a t i c D e s i g n in Cold Climate' An i n t e r n a t i o n a l c o n f e r e n c e of r a r i t y to be h e l d in m i d - w i n t e r and with p u b l i c p a r t i c i p a t i o n , we look f o r w a r d to s e e i n g many of you at this w o r t h y event.

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